Nov 14 2012
Topics Covered
IntroductionChemical CompositionPhysical PropertiesOther DesignationsFabrication and Heat Treatment Machinability Forming Welding Forging Cold Working Annealing HardeningApplications
Introduction
Super alloys or high performance alloys have the capacity to function under very high temperatures and extreme mechanical stress, and also where high surface stability is required. They have good creep and oxidation resistance.
Super alloys contain many elements in a variety of combinations so as to achieve the desired result. Strengthening of super alloys is performed by solid-solution hardening, work hardening, and precipitation hardening methods.
There are three types of alloys, namely cobalt-base, nickel-base, and iron-base. All of these can be used at temperatures above 540°C (1000°F).
Super alloy AF.550 is also known as Ferralium alloy 255. It is an improved stainless steel of chromium-iron-nickel. It has excellent chemical corrosion resistance and erosion resistance.
The following datasheet will provide more details about super alloy AF.550.
Chemical Composition
The following table shows the chemical composition of super alloy AF.550.
| Element |
Content (%) |
| Chromium, Cr |
24-27 |
| Nickel, Ni |
4.5-6.5 |
| Molybdenum, Mo |
2.9-3.9 |
| Copper, Cu |
1.5-2.5 |
| Manganese, Mn |
1.5 max |
| Silicon, Si |
1 max |
| Nitrogen, N |
0.1-0.25 |
| Carbon, C |
0.04 max |
| Phosphorus, P |
0.04 max |
| Sulfur, S |
0.03 max |
| Iron, Fe |
Remainder |
Physical Properties
The physical properties of super alloy AF.550 are outlined in the following table.
| Properties |
Metric |
Imperial |
| Density |
7.80 g/cm³ |
0.282 lb/in³ |
| Melting point |
1399°C |
2550°F |
Other Designations
Equivalent materials to super alloy AF.550 are provided below:
- ASTM A240
- ASTM A479
- ASTM A789
- ASTM A790
- ASTM A815
Fabrication and Heat Treatment
Machinability
Although super alloy AF.550 is harder than many other stainless steels, it is machinable. The traditional methods can be used for machining. It is better to use slow speeds and provide constant feeds to prevent work hardening.
Forming
Super alloy AF.550 can be formed using conventional methods.
Welding
Super alloy AF.550 is weldable using all the conventional methods.
Forging
Forging of super alloy AF.550 should be performed in the range of 1215-927°C (2220-1700°F). Re-annealing must be performed after forging to help recover good corrosion resistance.
Cold Working
Super alloy AF.550 can be easily cold worked as it is a ductile alloy. It is similar to the stainless steels except that it is stiffer. Conventional methods can be used for cold working. This must be followed by annealing to help recover good corrosion resistance.
Annealing
Super alloy AF.550 can be annealed at 1038°C (1900°F) and followed by air cooling.
Hardening
Super alloy AF.550 can be hardened by cold working only.
Applications
Super alloy AF.550 is applied in chemical process equipment in which chlorides or phosphoric acid are used. The erosion resistance feature of this alloy enables it to also be used for pumps and valves handling hot slurries that may be abrasive/corrosive.